Wheat rust overwinters in Arkansas crop

Jason Kelley | Mar 18, 2005

The small but tough Arkansas wheat crop is now facing a challenge from stripe rust and leaf rust. Like Texas, Louisiana and Oklahoma — Arkansas is finding higher-than-normal levels of the rusts overwintering in the state. Based on reports from county agents, consultants and others, I suspect the rusts have overwintered as far north as Cross County in northeast Arkansas.

Southwest Arkansas appears to have the most active rust, with stripe rust very active in certain fields. Fields with high-yield potential are being evaluated for a fungicide application to stop the rust epidemic.

Spraying fields during early March is almost unheard of in recent years, and two fungicide applications will likely be necessary for the season. This is a field-by-field judgment call. I do not make blanket recommendations in years like this with regard to fungicides.

Gene Milus, University of Arkansas professor of plant pathology and a nationally known wheat disease expert, said, “Most years in Arkansas, we can control the rusts and other spring foliar diseases with a single, well-timed fungicide application. Usually this will occur in April, when wheat reaches the booting stage, and the fungicide simply protects the upper leaves during heading and grain fill.

“But this is a very unusual year. The rusts have overwintered in Arkansas and are active earlier than normal because of the mild winter, making early damage — especially from stripe rust — a real concern on the better wheat fields. In these cases, two fungicide applications may be required to prevent a disease runaway.” Given current wheat prices, two fungicide applications at an estimated total cost of $30 per acre, will make profit on these fields very difficult to realize.

The alternative of inadequate or no control, however, could cost even more. This is why it is very important to select varieties based on high yield potential and disease resistance — at least for the rusts.

Currently, Southern States 560 and Croplan Genetics 554W seem to be most affected by stripe rust in southwest Arkansas, but other varieties may also be affected. Fields of AGS 2000 in the area have remained relatively unaffected so far.

Since the rust fungi can change from year to year, it is important to report any rust findings to local county Extension agents so we can keep track of shifts.

And it is critical that growers stay updated on the latest ratings and other observations reported each year by the University of Arkansas Division of Agriculture and university scientists in surrounding states. A good way to stay on top of things in Arkansas is through the local county Extension office and by receiving Arkansas Wheat, an electronic newsletter issued March through May each year and available on the Internet at http://www.aragriculture.org/News/wheat_update/default.asp[1]. The annual Wheat Update is also available at this site.

Jason Kelley is the Arkansas Extension agronomist for wheat and feed grains.